1. Field of the Invention
The present invention relates to a throttle valve control system for controlling operation of a throttle valve in an internal combustion engine of a vehicle.
2. Description of the Prior Art
Recently, as the result of the decrease in the power output of the internal combustion engines of exhaust emission controlled automotive vehicles and the tendency of the ordinary passenger cars to become increasingly large and heavy, deterioration of the driving feeling has become a matter of concern. The speed regulation of a vehicle is conventionally accomplished through the depression of the accelerator pedal by the driver which operates the throttle valve to vary the amount of mixture drawn into the engine and thereby vary the power output or rotational speed of the engine and consequently the movement of the accelerator pedal representing the driver's will must be accurately reflected in the rotation of the throttle valve. It is also necessary that in place of only one kind of linear relationship, the characteristic between the movement of the accelerator pedal (hereinafter referred to as the accelerator position) and the opening of the throttle valve must be varied in many different ways in accordance with the output and operating conditions of the engine. Further, while the movement of the accelerator pedal is usually adjusted chiefly by the movement of the driver's ankle which is limited to a narrow range of about 10 cm in terms of the movement of the toe and this movement of the accelerator pedal is changed into a rotary motion or reciprocal motion through a link mechanism and is then transmitted to the throttle valve of the carburetor, this link mechanism enters into the bonnet beneath the driver's seat and extends to the carburetor of the engine. Thus, the link mechanism passes through the relatively limited portions with the result that the transmission of the motion is extremely complicated. For instance, in the case of a known type of link mechanism, the movement of the accelerator pedal must be subjected to a number of changes, namely, it must be changed into rotary motion, rotary motion, reciprocating motion, rotary motion, reciprocating motion and rotary motion again before it can be transmitted to the carburetor throttle valve and consequently the movement of the ankle which reflects the driver's will, i.e., the movement of the accelerator pedal cannot be accurately transmitted to the throttle valve. In other words, since the movement of the accelerator pedal must be subjected to a number of changes, no linear proportionality holds between the movement of the accelerator pedal and the rotation of the throttle valve and moreover looseness of the motion changing joints or the like tends to produce hysteresis. Furthermore, in the case of the wire mechanism, there is a disadvantage that due to the necessity to eliminate looseness of the wire or due to the effect of friction, considerable force is required to transmit the movement of the accelerator pedal and this causes the driver to feel that the accelerator pedal is stiff. Still further, with either of the link mechanism and the wire mechanism, it is not an easy matter to adjust the range of movement of the accelerator pedal to an amount that suits the driver. With either of the link mechanism and the wire mechanism, it is possible to obtain only one kind of characteristic between the accelerator position and the throttle valve opening and it is extremely difficult to cause the characteristic to vary in accordance with varying operating conditions of the engine.